A sorting system to sort an article that is a delivery object is known. The sorting system detects passing of an article which is conveyed and sorts the article, based on address information and so on read out from the article. A transmission type optical sensor is used for detection of passing of an article. The transmission type optical sensor can detect a plurality of articles which are conveyed in line along a conveying direction at intervals not less than a prescribed length one by one.
Sometimes, the sorting system cannot detect a plurality of articles which are conveyed obliquely in line one by one. That is, the sorting system cannot find a separation position between a plurality of the articles which are conveyed obliquely in line, and may detect a plurality of the articles as one article. In such a case, if a sorting bar code or a delivery destination address is recognized from only one article out of a plurality of the articles, the plurality of the articles is erroneously sorted as one article. That is, the plurality of the articles is collectively sorted into one shooter erroneously.
When a plurality of articles cannot be sorted into separate sorting destinations, the recognition processing of a previous stage thereof runs to waste. That is, the inefficient utilization of computation resources is generated.